1. Field of the Invention
This invention relates to a cooling system controller for internal combustion engines which can be used for a two-circuits cooling system in which the passageway of cooling water is divided into a cylinder head side circuit and a cylinder block side circuit.
2. Prior Art
In the Japanese Laid-open Patent Bulletin of Toku-kai No. sho 59-215915 (215915/1984), there is proposed a cooling system for internal combustion engines wherein; a cooling water circuit for cylinder head and a cooling water circuit for cylinder block are disposed separately; the temperature of cooling water at the cylinder head side is controlled to be low temperature with the thermostats which are provided to each circuit respectively so that the knocking control and the filling efficiency control are well performed and; the temperature of cooling water at the cylinder block side is controlled to be high temperature so that the temperature of lubrication oil is increased and its friction degree is decreased by reduction of viscosity.
Further, in the Japanese Laid-open Utility Model Bulletin of Jitsu-kai No. sho 60-102422 (102422/1985), there is proposed a cooling system for water-cooled engines in which the setting of temperature of each circuit is performed by a thermostat provided to each circuit as well as by the difference of water flow rate owing to the difference of cross section area between two branch circuit pipes each of which is branched from a common pipe.
The above-described conventional systems, however, have the following drawbacks. Namely, the temperature control by using thermostat has the drawbacks that it cannot follow the variation of vehicle running conditions which always varies during the vehicle run and that an optimum temperature control in accordance with various vehicle running conditions cannot be performed, as the thermostat has drawbacks that its response capability is not high and its set-temperature cannot be changed.
The control system using the difference of cross section area of the branch pipe, too, cannot supply necessary volume of water though it can adjust the water flow ratio between two passageways. Namely, since the water pump as the water flow source is driven by a crank shaft of engine and the water flow rate corresponds to the engine rotation rate, the volume of cooling water supplied to each passageway depends on the rotation rate of the engine and the optimum control of flow rate in accordance with the vehicle running conditions cannot be performed.
A system which intends to improve the response speed is proposed in the Japanese Laid-open Patent Bulletin Toku-kai No. sho 59-213918 (213918/1984). This system employs a control method wherein an electronic control unit judges the signal of the water temperature sensor to position a movable control part of the water flow control valve with a diaphragm by VSV. But this system, too, has a drawback in the accuracy of control. Namely, the conversion of a suction degree to a stroke degree by using diaphragm tends to have a bad influence with the accurate positioning, owing to the friction between parts of the valve and the dynamic or static pressure in the water flow circuit.
A control system which intends to make the set-temperature of thermostat valve to be variable is proposed in the Japanese Laid-open Patent Bulletin Toku-kai No. sho 60-128924 (128924/1985). In this system, the valve open temperature of wax-type thermostat is adjusted by a diaphragm which operates depending on the suctioning force of a suction pipe. But this system, too, has a drawback in the accuracy of control of set-temperature.